The present invention relates generally to commercial printing operations, especially such operations utilizing engraved anilox printing rolls. More particularly, the present invention relates to devices commonly referred to in the industry asxe2x80x9cproofersxe2x80x9d used for producing sample test printings of inks, coatings and the like preparatory to the implementation of a commercial printing operation, e.g., for determining appropriate printing roll characteristics and parameters for color selection or color matching purposes.
In conventional flexographic printing operations, it is widely recognized that the consistent delivery of a uniformly thin film of ink to the printing plate is critical to achieving consistent satisfactory print quality and, toward that end, the physical characteristics of the anilox roll largely determine the thinness and uniformity of the ink film transferred to the printing plate. Generally speaking, so long as a minimum acceptable density of ink is consistently maintained, it is desirable that the ink film delivered by the anilox roll be as thin as possible in order to provide optimal contrast and print fidelity.
As is known, anilox rolls are engraved, typically either by a mechanical or a laser engraving operation, to produce an array of recesses circumferentially about the peripheral surface of the roll, commonly referred to asxe2x80x9ccells.xe2x80x9d Somewhat overly simplified, the principal characteristics of anilox rolls which determine the thickness or thinness of the ink film are the size, shape and depth of each cell, which determine the volume of ink each cell can contain, and the relative arrangement and spacing of the cells over the peripheral roll surface, generally measured and expressed as the number of cells per linear inch of the roll surface and commonly referred to as thexe2x80x9cline screenxe2x80x9d of a given roll.
In view of these variables in anilox rolls which affect the results in general and the quality in particular of a printing operation, the selection of the appropriate combination of physical characteristics for an anilox roll to accomplish a given printing operation is not necessarily capable of being precisely predicted and, hence, is currently as much an art as a science in actual practice. It is accordingly commonplace to perform test printings with differing anilox rolls preparatory to setting up and implementing a commercial printing operation in order to determine and verify the optimal necessary and desirable roll characteristics, e.g., cell size and shape and line screen, particularly for color testing and matching purposes.
Because of the large size of flexographic printing presses and the anilox rolls used therein, it is difficult, expensive and impractical to perform multiple test runs at the full scale of commercial equipment. Hence, miniature hand-held manually operable devices commonly referred to asxe2x80x9cproofersxe2x80x9d have been developed to enable more simplified print testing runs to be performed. One example of a conventional commercially available proofing device of this type is thexe2x80x9cPrecision Prooferxe2x80x9d marketed by Precision Proofing Company, located in West Monroe La.,
While these conventional proofing devices are generally satisfactory in operation at least from the standpoint that the results of such proofers are typically more accurate and reliable than the selection of anilox rolls without preliminaryxe2x80x9cproofingxe2x80x9d tests, the known conventional proofers are still considerably less accurate and reliable than the flexographic printing industry desires and there remains an unacceptable margin for error between the results achieved with a proofer and the ultimate outcome of the commercial printing operation subsequently set up based on the use of such proofers. One of the most fundamental deficiencies of known proofers is that the miniaturized anilox rolls used therein are only mechanically engraved, which has significant physical limitations in simulating the higher line screens conventionally used in flexographic printing operations performed with laser-engraved anilox rolls. Further, even with such proofing devices, there remains the concern for the time required to exchange rolls in order to perform multiple tests. Thus, there exists a substantial need within the relevant industry for a proofer which more closely simulates a commercial printing operation and enables quicker, more precise determinations to be made in selecting an anilox roll for a commercial printing operation.
It is accordingly an objection of the present invention to provide an improved proofing device which addresses the above-described deficiencies of known conventional proofers.
Briefly summarized, the present invention addresses this objective by providing a manually operable proofer basically comprising a frame adapted for manual movement over a printable substrate with a printing roll rotatably supported from the frame for rotatably delivering an imprinting onto the substrate as the frame is moved thereover. Preferably, the printing roll is an anilox roll having an array of recessed ink-collecting cells circumferentially thereabout and, most preferably, the cells are laser engraved into the periphery of the printing roll. It is further preferred that a transfer roll be rotatably supported by the frame adjacent the printing roll for peripheral surface contact therewith, thereby to be rotated in synchronism with one another.
According to one feature of the present invention, the printing roll is rotatably supported on a carriage which is mounted on the frame for movement between an operative position wherein the printing roll is secured in a disposition for forming the imprinting on the substrate as the frame moves thereover and an inoperative position wherein the printing roll is accessible to be removable for cleaning or exchange with a substitute printing roll. More particularly, the carriage comprises spaced support walls with aligned recesses therein to respectively receive opposite ends of the printing roll. In this manner, the spaced support walls of the carriage form a cradle portion which is disposed within the frame when the carriage is in its operative position in order to retain the printing roll within the cradle portion but is exposed outwardly of the frame when the carriage is in its inoperative position for easy removal of the printing roll from the spaced recesses.
In accordance with another aspect of the present invention, a doctor blade is supported by the carriage, preferably between the spaced support walls, for peripheral engagement with the printing roll in the operative position of the carriage. A torque screw or other suitable arrangement is provided for biasing the doctor blade so as to exert a predetermined peripheral engagement force against the printing roll in its operative position. It is further preferred that the doctor blade be releasably mounted to the carriage to enable disassembly from the carriage when necessary or desirable.
According to another feature of the present invention, the printing roll is formed with at least two distinct circumferential regions or bands each formed of a differing array of ink-collecting cells, e.g., having differing cell sizes, shapes and/or line screens. In this manner, each individual operation of the proofer effectively produces at least two or more distinct sample test printings, thereby reducing the number of exchanges of printing rolls necessary to complete a proofing operation.
The frame of the proofer also preferably includes a handle for manually controlling movement of the frame and, most preferably, the handle has a retaining portion spring-biased into a first position for engagement with the carriage in its operative position for retaining the carriage therein and yieldable into a second position withdrawn from the carriage for permitting movement of the carriage into its inoperative position.
Other characteristics, features and advantages of the proofer of the present invention will be described and understood from the following disclosure of a preferred embodiment of the proofer with reference to the accompanying drawings.